Controllable space velocity reactor and process

ABSTRACT

Disclosed is an apparatus and process for controlling space velocity in a fluidized catalytic conversion reactor. The catalyst flux rate can be adjusted during the process of the reaction to adjust the space velocity and maintain a fast fluidized flow regime therein. The set parameter in the reactor may be pressure drop which is proportional to catalyst density.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a Continuation-In-Part of copendingapplication Ser. No. 10/125,468 filed Apr. 18, 2002 and aContinuation-In-Part of copending application Ser. No. 09/670,661 filedSep. 27, 2000, which is a Division of application Ser. No. 09/378,416filed Aug. 20, 1999, now U.S. Pat. No. 6,166,282, the contents of whichapplications are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a catalytic conversionreactor and process utilizing a catalytic reaction zone with acontrollable space velocity.

BACKGROUND OF THE INVENTION

[0003] In many catalytic reactions, it is important that reactants bewell mixed with catalyst to afford sufficient opportunity for thereactant to contact the catalyst. Fluidized reactors have been designedto ensure adequate mixing of catalyst and reactants. Fluidized reactorsare designed to ensure that the reactants are in contact with thecatalyst for sufficient time to allow for the reaction to proceed.However, in many catalyzed reactions the reactants should not remain incontact with catalyst too long or overconversion can occur which cangenerate undesirable byproducts and degrade product quality. This isespecially true when the reaction involves hydrocarbons of whichoverreaction can cause excess generation of coke, inhibiting catalystactivity and selectivity.

[0004] Space velocity typically referred to as weight hourly spacevelocity (WHSV) is crucial to ensuring that reactants and catalyst arein contact for the optimal duration. Space velocity is a reactioncondition that is important when rapid reaction times are involved suchas monomolecular catalytic cracking reactions or rapid catalyticconversion reactions. The catalyst and reactants need to make contact,but excessive contact time will cause additional undesirable reaction tooccur. Space velocity is calculated by Formula 1: $\begin{matrix}{{WHSV} = \frac{M_{f}}{m_{c}}} & (1)\end{matrix}$

[0005] where WHSV is the weight hourly space velocity, M_(f) is the massflow rate of feed to the reactor and m_(c) is the mass of catalyst inthe reactor. Space time is the inverse of space velocity. The mass ofcatalyst, m_(c), can be determined by Formula 2: $\begin{matrix}{m_{c} = \frac{\Delta \quad {P \cdot V}}{h}} & (2)\end{matrix}$

[0006] where ΔP is the pressure drop over the height, h, of the reactorand V is the volume of the reactor. The ratio of pressure drop andheight is the catalyst density in the reactor: $\begin{matrix}{\rho_{c} = \frac{\Delta \quad P}{h}} & (3)\end{matrix}$

[0007] Hence, combining Formulas 2 and 3:

m _(c)=ρ_(c) ·V  (4)

[0008] Accordingly, both density, ρ_(c), and space velocity, WHSV, arefunctions of pressure drop, ΔP. From Formula 4, the relationship ofspace velocity and volume is shown in Formula 5: $\begin{matrix}{{WHSV} = \frac{M_{f}}{\rho_{c}V}} & (5)\end{matrix}$

[0009] Catalyst flux is determined by Formula 6: $\begin{matrix}{\omega_{c} = \frac{M_{c}}{A}} & (6)\end{matrix}$

[0010] where ω_(c) is catalyst flux, M_(c) is the mass flow rate ofcatalyst and A is the cross sectional area of the reactor. Additionallythe product of height, h, and cross-sectional area, A, when constant, ofthe reactor is the reactor volume, V:

V=h·A  (7)

[0011] The mass flow rate of feed, M_(f), to the reactor is calculatedby Formula 8:

M _(f) =v _(f)·ρ_(f) ·A  (8)

[0012] where v_(f) is the superficial gas velocity of the feed, ρ_(f) isthe density of the feed and A is the cross sectional area of the reactorat which the velocity is measured. Hence, substituting Formulas 2, 7 and8 into Formula 1 for constant cross-sectional reactor area yieldsformula 9: $\begin{matrix}{{WHSV} = \frac{v_{f}\rho_{f}}{\Delta \quad P}} & (9)\end{matrix}$

[0013] Residence time is a reaction condition that is important when thereaction is not as rapid. The catalyst and reactants need to soaktogether to ensure catalyst and reactants are in contact and for asufficient period of time to allow the reaction to occur. Residencetime, T_(r), is calculated by Formula 10: $\begin{matrix}{T_{r} = \frac{V}{Q_{f}}} & (10)\end{matrix}$

[0014] where Q_(f) is the actual volumetric flow rate of feed at reactorprocess conditions of temperature and pressure. The volumetric flowrate, Q_(f), to the reactor is calculated by Formula 11:

Q _(f) =v _(f) ·A  (11)

[0015] Substituting Formulas 7 and 11 into Formula 10 for constantcross-sectional reactor area yields: $\begin{matrix}{T_{r} = \frac{h}{v_{f}}} & (12)\end{matrix}$

[0016] In a fluidized catalytic reactor, the flow characteristics may beconsidered to assure space velocity or residence time is optimal.

[0017] Two types of fluidization regimes typically used in fluidizedcatalytic reactors are a transport flow regime and a bubbling bed.Transport flow regimes are typically used in FCC riser reactors. Intransport flow, the difference in the velocity of the gas and thecatalyst, called the slip velocity, is relatively low, typically lessthan 0.3 m/s (1.0 ft/s) with little catalyst back mixing or hold up.Slip velocity is calculated by formula 9: $\begin{matrix}{v_{s} = {\frac{v_{f}}{ɛ} - v_{c}}} & (13)\end{matrix}$

[0018] where v_(s) is the slip velocity, v_(f) is the superficial gasvelocity of the feed, v_(c) is the catalyst velocity and ε is the voidfraction of the catalyst. Another way to characterize flow regimes is byslip ratio which is the ratio of actual density in the flow zone to thenon-slip catalyst density in the flow zone. The non-slip catalystdensity is calculated by the ratio of catalyst flux to the superficialgas velocity as in formula 10: $\begin{matrix}{\rho_{cns} = \frac{\omega_{c}}{v_{f}}} & (14)\end{matrix}$

[0019] whereρ_(cns) is the non-slip catalyst density in the flow zone,ωc_(c) flux of the catalyst and v_(f) is the superficial gas velocity ofthe feed. The slip ratio is proportional to the hold up of catalyst inthe flow zone. Typically, a slip ratio for a transport flow regime doesnot reach 2.5. Consequently, the catalyst in the reaction zone maintainsflow at a low density and very dilute phase conditions. The superficialgas velocity in transport flow is typically greater than 3.7 m/s (12.0ft/s), and the density of the catalyst is typically no more than 48kg/m³ (3 lb/ft³) depending on the characteristics and flow rate of thecatalyst and vapor. In transport mode, the catalyst-vapor mixture ishomogeneous without vapor voids or bubbles forming in the catalystphase.

[0020] Fluidized bubbling bed catalytic reactors are also known. In abubbling bed, fluidizing vapor forms bubbles that ascend through adiscernible top surface of a dense catalyst bed. Only catalyst entrainedin the vapor exits the reactor with the vapor. The superficial velocityof the vapor is typically less than 0.5 m/s (1.5 ft/s) and the densityof the dense bed is typically greater than 480 kg/m³ (30 lb/ft³)depending on the characteristics of the catalyst. The mixture ofcatalyst and vapor is heterogeneous with pervasive vapor bypassing ofcatalyst.

[0021] Intermediate of dense, bubbling beds and dilute, transport flowregimes are turbulent beds and fast fluidized regimes. U.S. Pat. No.4,547,616 discloses a turbulent bed used in a reactor for convertingoxygenates to olefins. In a turbulent bed, the mixture of catalyst andvapor is not homogeneous. The turbulent bed is a dense catalyst bed withelongated voids of vapor forming within the catalyst phase and a lessdiscernible surface. Entrained catalyst leaves the bed with the vapor,and the catalyst density is not quite proportional to its elevationwithin the reactor. The superficial velocity is between about 0.5 andabout 1.3 m/s (1.5 and 4.0 ft/s), and the density is typically betweenabout 320 and about 480 kg/m³ (20 and 30 lb/ft³) in a turbulent bed.

[0022] U.S. Pat. No. 6,166,282 discloses a fast fluidized flow regimefor oxygenate conversion. Fast fluidization defines a condition offluidized solid particles lying between the turbulent bed of particlesand complete particle transport mode. A fast fluidized condition ischaracterized by a fluidizing gas velocity higher than that of a densephase turbulent bed, resulting in a lower catalyst density and vigoroussolid/gas contacting. In a fast fluidized zone, there is a net transportof catalyst caused by the upward flow of fluidizing gas. The superficialcombustion gas velocity for a fast fluidized flow regime isconventionally believed to be between about 1.1 and about 2.1 m/s (3.5and 7 ft/s) and the density is typically between about 48 and about 320kg/m³ (3 and 20 lb/ft³). Catalyst exits the reaction zone a small amountslower than the vapor exiting the reaction zone. Hence, for a fastfluidized flow regime the slip velocity is typically greater than orequal to 0.3 m/s (1.0 ft/s) and the slip ratio is greater than or equalto 2.5 for most FCC catalysts. Fast fluidized regimes have been used inFCC combustors for regenerating catalyst and in coal gasification.

[0023] The conversion of hydrocarbon oxygenates to olefinic hydrocarbonmixtures is accomplished in a fluidized catalytic reactor. Suchoxygenates to olefins reactions are rapidly catalyzed by molecularsieves such as a microporous crystalline zeolite and non-zeoliticcatalysts, particularly silicoaluminophosphates (SAPO). Numerous patentsdescribe this process for various types of these catalysts: U.S. Pat.No. 3,928,483; U.S. Pat. No. 4,025,575; U.S. Pat. No. 4,252,479; U.S.Pat. No. 4,496,786; U.S. Pat. No. 4,547,616; U.S. Pat. No. 4,677,243;U.S. Pat. No. 4,843,183; U.S. Pat. No. 4,499,314; U.S. Pat. No.4,447,669; U.S. Pat. No. 5,095,163; U.S. Pat. No. 5,191,141; U.S. Pat.No. 5,126,308; U.S. Pat. No. 4,973,792 and U.S. Pat. No. 4,861,938.

[0024] The oxygenates to olefins catalytic process may be generallyconducted in the presence of one or more diluents which may be presentin the hydrocarbon oxygenate feed in an amount between about 1 and about99 mol-%, based on the total number of moles of all feed and diluentcomponents fed to the reaction zone (or catalyst). Diluents include, butare not limited to, helium, argon, nitrogen, carbon monoxide, carbondioxide, hydrogen, water, and hydrocarbons such as methane, paraffins,aromatic compounds, or mixtures thereof. U.S. Pat. No. 4,861,938 andU.S. Pat. No. 4,677,242 particularly emphasize the use of a diluentcombined with the feed to the reaction zone to maintain sufficientcatalyst selectivity toward the production of light olefin products,particularly ethylene.

[0025] U.S. Pat. No. 6,023,005 discloses a method for selectivelyconverting hydrocarbon oxygenates to light olefins in which desirablecarbonaceous deposits are maintained on the total reaction volume ofcatalyst by regenerating only a portion of the total reaction volume ofcatalyst and mixing the regenerated portion with the unregenerated totalreaction volume of catalyst. The method incorporates a fluidizedcatalytic bed reactor with continuous regeneration. In a preferredarrangement, the oxygenate feed is mixed with regenerated catalyst andcoked catalyst at the bottom of a riser and the mixture is lifted to adisengaging zone. In the disengaging zone, coked catalyst is separatedfrom the gaseous materials by means of gravity or cyclone separators. Aportion of the coked catalyst to be regenerated is sent to a strippingzone to recover adsorbed hydrocarbons. Stripped spent catalyst is passedto a regenerator.

[0026] U.S. Pat. No. 4,547,616 discloses an improvement in a process forthe conversion of hydrocarbon oxygenates to olefins by the operation ofa turbulent bed at elevated temperatures and controlled catalystactivity. The turbulent bed is maintained in a vertical reactor columnto achieve good mixing at a velocity greater than the dense bedtransition velocity to a turbulent regime and less than transportvelocity for the average catalyst particle. The superficial fluidvelocity is disclosed in a range between about 0.3 to 2 meters persecond. Provision is made for passing partially regenerated catalyst tothe reactor fluidized bed of catalyst beneath the upper interface andsufficiently below to achieve good mixing in the fluid bed.

[0027] Another typical fluidized catalytic reaction is a fluidizedcatalytic cracking (FCC) process. An FCC process is carried out bycontacting the starting material whether it be vacuum gas oil, reducedcrude, or another source of relatively high boiling hydrocarbons with acatalyst made up of finely divided or particulate solid material. Thecatalyst is fluidly transported by passing gas through it at sufficientvelocity to produce a transport flow regime. Contact of the oil with thefluidized catalytic material catalyzes the cracking reaction. Thecracking reaction deposits coke on the catalyst. Catalyst exiting thereaction zone is spoken of as being “spent”, i.e., partially deactivatedby the deposition of coke upon the catalyst. Coke is comprised ofhydrogen and carbon and can include other materials in trace quantitiessuch as sulfur and metals that enter the process with the startingmaterial. Coke interferes with the catalytic activity of the spentcatalyst by blocking acid sites on the catalyst surface where thecracking reactions take place. Spent catalyst is traditionallytransferred to a stripper that removes adsorbed hydrocarbons and gasesfrom catalyst and then to a regenerator for purposes of removing thecoke by oxidation with an oxygen-containing gas. The regenerator mayoperate with a bubbling bed, turbulent bed or fast fluidized flowregime. Such regenerators using a fast flow regime are calledcombustors. However, in a regenerator or combustor, coke is burned fromthe catalyst. The catalyst does not provide a catalytic function otherthan with regard to oxidation. An inventory of catalyst having a reducedcoke content, relative to the spent catalyst in the stripper,hereinafter referred to as regenerated catalyst, is collected for returnto the reaction zone. Oxidizing the coke from the catalyst surfacereleases a large amount of heat, a portion of which escapes theregenerator with gaseous products of coke oxidation generally referredto as flue gas. The balance of the heat leaves the regenerator with theregenerated catalyst. The fluidized catalyst is continuously circulatedbetween the reaction zone and the regeneration zone. The fluidizedcatalyst, as well as providing a catalytic function in the reactionzone, acts as a vehicle for the transfer of heat from zone to zone. TheFCC processes, as well as separation devices used therein are fullydescribed in U.S. Pat. No. 5,584,985 and U.S. Pat. No. 4,792,437.Specific details of the various reaction zones, regeneration zones, andstripping zones along with arrangements for conveying the catalystbetween the various zones are well known to those skilled in the art.

[0028] The FCC reactor catalytically and thermally cracks gas oil orheavier feeds into a broad range of products. Cracked vapors from theFCC unit enter a separation zone, typically in the form of a maincolumn, that provides a gas stream, a gasoline cut, light cycle oil(LCO) and clarified oil (CO) which includes heavy cycle oil (HCO)components. The gas stream may include dry gas, i.e., hydrogen and C₁and C₂ hydrocarbons, and liquefied petroleum gas (“LPG”), i.e., C₃ andC₄ hydrocarbons. The gasoline cut may include light, medium and heavygasoline components. A major component of the heavy gasoline fractioncomprises condensed single ring aromatics. A major component of LCO iscondensed bicyclic ring aromatics.

[0029] Subjecting product fractions to additional reactions is usefulfor upgrading FCC product quality. The recracking of heavy productfractions from an initially cracked FCC product is one example.Typically, in recracking, cracked effluent from a riser of an FCCreactor is recontacted with catalyst at a second location to cleavelarger molecules down into smaller molecules. For example, U.S. Pat. No.4,051,013 discloses cracking both gasoline-range feed and gas oil feedin the same riser at different elevations. Such reactions are relativelyrapid. WO 01/00750 A1 discloses introducing gasoline feed and FCC feedat different elevations in a riser reactor, separating the crackedproduct and recycling portions thereof back to the same riser reactor.Other types of reactions to upgrade FCC product fractions are lessrapid.

[0030] The above-described hydrocarbon catalytic conversion processesare sensitive to underreaction and overreaction which both degradeproduct quality. Use of a fast fluidized flow regime assures thoroughmixing of catalyst and feed to catalyze the reaction. Hence, we soughtto provide an improved fluidized non-oxidative catalytic hydrocarbonconversion process and apparatus that can provide a fast fluidized flowregime at adjustable flow conditions that will enhance the conversion tothe desired products. Additionally, we sought to provide a reactor thatcan accommodate the varying demands on space velocity and residence timebased on different feed composition and desired products.

SUMMARY OF THE INVENTION

[0031] We have discovered a reactor and process for controlling spacevelocity in a fluidized catalytic reactor. Catalyst density in a fastfluidized flow regime is sensitive to catalyst flux. Space velocity is afunction of catalyst density. Therefore, it is possible to adjust thecatalyst circulation rate to achieve the desired space velocity toeffect catalyst to feed contacting at highly effective gas-solid, mixingconditions. Moreover, the catalyst circulation rate can be controlledbased on the pressure drop in the reactor to maintain or achieve adesired space velocity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a schematic drawing of a fluidized catalytic reactor foruse in the present invention.

[0033]FIG. 2 is a schematic drawing of an alternative embodiment of thepresent invention.

[0034]FIG. 3 is a cross-sectional view taken along segment 3-3 in FIG.2.

[0035]FIG. 4 is a schematic drawing of a further alternative embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0036] We have discovered a catalytic reactor that can be used to obtainthorough mixing of fluid reactants and particulate catalyst whilecontacting the catalyst and fluid reactants together for an adjustablyoptimal time. Hence, desirable reactions may occur without underreactingor overreacting to degrade the quality of the product composition forvarying feeds and varying reactions. For example, in a fluidizedcatalytic reactor for upgrading naphtha that may be obtained from an FCCcut, we have found that better mixing between the feed and the catalystpromotes (hydrogen transfer reactions and catalytic cracking reactionswhile reducing the undesirable generation of coke and dry gas. Use of afast fluidized catalytic conversion zone provides such thorough mixing.We have also found that in catalytic conversion of hydrocarbonoxygenates to olefins, use of a fast fluidized zone significantlyreduces catalyst inventory compared to dense fluidized catalyticreactions. However, we have found that maintaining a fast fluidizedreaction zone may be difficult. Fast fluidized combustion zones havebeen attempted in combustors for oxidizing coked catalyst from an FCCreactor zone but such combustors do not involve nonoxidative catalyticconversion. The main concern in a combustion zone is that the catalysthas sufficient residence time to burn off all of the coke. Fluidizedcatalytic conversion reactors particularly hydrocarbon catalyticconversion processes bring with it other flow considerations because thefeed is the primary fluidization medium and the reactant that isundergoing catalytic conversion to recoverable product. The selectivityand conversion of the gas phase reaction must be optimized. Selectivityand conversion are functions of temperature, residence time and spacevelocity. As indicated by Formulas 1 and 5, space velocity is related toboth catalyst and reactant feed flow rates and reactor volume. Formula11 indicates that residence time is related to reactor volume. Hence,this invention gives greater consideration to the flow characteristics,space velocity and residence time in a fluidized catalytic conversionreactor. Controlling these flow characteristics provides for achievingand maintaining a desired fluidization regime, particularly a fastfluidized flow regime.

[0037] The present invention may be described with reference to afluidized catalytic reactor 10 shown in FIG. 1. Although manyconfigurations of the present invention are possible, one specificembodiment is presented herein by way of example. All other possibleembodiments for carrying out the present invention are considered withinthe scope of the present invention.

[0038] In the embodiment of the present invention in FIG. 1, thecatalytic reactor 10 comprises a reactor section 12 and a separationsection 16 that may include a disengaging section 14. The contacting offeed and catalyst occurs in the reactor section 12 of the catalyticreactor 10. Control valves 18, 20 govern the rate of catalystcirculation to the reactor section 12. The control valve 18 governs theflow rate of regenerated catalyst from a catalyst regenerator 66 througha regenerated catalyst pipe 24 to the reactor section 12, and thecontrol valve 20 governs the flow rate of recycled catalyst through arecycle spent catalyst pipe 26 to the reactor section 12. The catalystflow rate through one or both of the control valves 18 and/or 20 isinversely proportional to the space velocity of reactants through thereactor section 12. Relative settings of the control valves 18, 20 areindependently adjusted also to obtain the desired temperature andmixture of the catalyst in the reactor section 12 that will contact thereactant feed. The multiple recycle spent catalyst pipes 26 may be usedto increase catalyst flux, and the recycle spent catalyst pipes 26 mayextend through the reactor 10 and particularly the reactor section 12.

[0039] In an embodiment, the regenerated catalyst from the regeneratedcatalyst pipe 24 and the recycled catalyst from the recycle spentcatalyst pipe 26 are mixed in a mixing pot 30 of the reactor section 12.A minimally reactive or non-reactive diluent, such as steam, isdistributed to the mixing pot 30 through a nozzle 32 to mix theregenerated and recycled catalyst before it contacts the feed. Themixing pot 30 enables adequate mixing and temperature equilibration ofrecycled and regenerated catalyst before it is introduced to the feed.This assures that the hot regenerated catalyst is moderated to a lowertemperature by thorough mixing and direct heat exchange with the coolerrecycled catalyst which has not been heated by regeneration. All or apart of the hot regenerated catalyst could cause thermal cracking orother undesirable byproduct generation if it were allowed to contact thefeed reactants without first undergoing thorough moderation. In anembodiment which does not utilize a catalyst regenerator, the mixing pot30 may not be necessary.

[0040] Feed reactants which may include hydrocarbons are introducedthrough a line 36 to a distributor 38 which distributes feed to thereactor section 12. The feed may be liquid that is vaporized in thereactor or vapor, in embodiments. The flow rate of feed through the line36 is governed by a control valve 40. The setting of the control valve40 also influences the space velocity and residence time. The feed rateto the reactor section 12 is directly proportional to the space velocityand inversely proportional to residence time.

[0041] Feed reactants from the distributor 38 contact fluidized catalystascending upwardly from the mixing pot 30. The feed reactants may alsoinclude diluent as is necessary to provide appropriate catalyticreaction conditions. In an embodiment, the feed reactants fluidize theascending catalyst to generate a fast fluidized bed in a catalyticreaction zone 22 of the reactor section 12. It may be in practice that adense bed forms at a base 42 of the reactor section 12 below the levelat which all of the catalyst is fluidized by the incoming feed reactantsin the catalytic reaction zone 22. In an embodiment, the catalyticreaction zone 22 extends between the distributor 38 and a top region 44,although catalytic activity may occur outside of the catalytic reactionzone 22. The top region 44 of the reactor section 12 has across-sectional area that decreases proportionally with height. The topregion 44 may take the form of a frustoconical section. The reducingcross-sectional area of the top region 44 serves to accelerate themixture of fluidized product and catalyst toward transport mode as theyexit the reactor section 12 and enter the transport conduit 46. Thetransport conduit 46 communicates the reactor section 12 with thedisengaging section 14. The transport conduit 46 may take the form of ariser. The transport conduit 46 should have a smaller cross-sectionalarea than the reactor section 12. Consequently, upon leaving thecatalytic reaction zone 22 and the reactor section 12, the productfluids and spent catalyst accelerate into a transport mode, thus givingthe spent catalyst and product fluids less time to further react orcrack into undesirable products. Entering transport mode also preventscatalyst from falling out of entrainment with the product fluids.

[0042] Spent catalyst and product ascend from the reactor section 12through the transport conduit 46 to the disengaging section 14. Thespent catalyst and vapor product exit through discharge openings 48(only one shown) in swirl tubes 50 to effect a primary, centripetalseparation of spent mixed catalyst from the vapor product. Separatedspent mixed catalyst settles into a dense bed 52 in the disengagingsection 14. The spent mixed catalyst in the dense bed 52 is then in anembodiment stripped over a series of baffles 54 by use of a strippingmedium such as steam entering through stripping nozzles 58 in astripping section 60 of the disengaging section 14. In an embodiment, afirst portion of the stripped spent catalyst exits the disengagingsection 14 through a spent catalyst pipe 62 at a flow rate that may begoverned by a control valve 64. The stripped spent catalyst may bedelivered to the regenerator 66. The regenerator 66 may be shared withanother fluidized catalytic system, such as an FCC system, in anembodiment. Alternatively, the spent catalyst pipe 62 may deliver spentcatalyst to another reactor. A second portion of the stripped spentcatalyst is withdrawn through the recycle spent catalyst pipe 26 at aflow rate governed by the control valve 20 and is delivered to themixing pot 30 where it is mixed with regenerated catalyst delivered fromthe regenerated catalyst pipe 24. Product vapors and entrained spentcatalyst exit from the disengaging section 14 through an outlet 68 tothe separation section 16 that contains at least one cyclone separator70. Alternatively, the separator section could comprise one or morecyclone separators 70 external to the disengaging section 14 and with aninlet directly connected to the outlet 68 and a dipleg 72 directlyconnected to the disengaging section 14 or the reactor section 12 byappropriate conduits. In an embodiment, the outlet 68 may be directlyconnected to the cyclone separators 70. The entrained spent catalyst iscentripetally separated from product vapors in the cyclone separators70. Separated catalyst exits through the dipleg 72 into a dense catalystbed 74 which may be fluidized (not shown). In an embodiment, spentcatalyst in the dense catalyst bed 74 enters into the stripping section60 of the disengaging section 14 through ports 76. Alternatively, thespent catalyst in the dense catalyst bed 74 may be removed through thepipes 26, 62 without undergoing stripping. Product fluids are withdrawnfrom the cyclone separators 70 through outlet conduits 78 and arerecovered in a line 80.

[0043] Referring to the reactor 10 of the present invention shown inFIG. 1, the space velocity may be changed in the reactor section 12 byincreasing or decreasing the rate of delivery of catalyst to the reactorsection 12. This can be done by adjusting the control valve 20 to changethe flow rate of spent catalyst through the recycle spent catalyst pipe26 into the mixing pot 30 and/or adjusting the control valve 18 tochange the flow rate of regenerated catalyst through the regeneratedcatalyst pipe 24 into the mixing pot 30 of the reactor section 12.Increasing the catalyst flow rate through one or both of the controlvalves 18, 20 into the reactor section 12 decreases the weight hourlyspace velocity in the reactor section 12 while decreasing the flow ratethrough one or both of the control valves 18, 20 increases the weighthourly space velocity. The total flow rate of catalyst to the reactorsection 12 through the pipes 24, 26 is directly proportional to catalystflux.

[0044] Another way to control the weight hourly space velocity is toincrease or decrease the feed flow rate through the control valve 40 onthe feed line 36. Increase of the feed flow rate is directly related tothe superficial velocity (v_(f)). However, the feed flow rate istypically left constant.

[0045] Lower superficial gas velocities have a greater tendency togenerate a dense bed as catalyst flux increases; whereas, highersuperficial gas velocities have a lower tendency to generate a dense bedas catalyst flux increases. The desired fast-fluidized flow regime inwhich the greatest degree of mixing of catalyst and reactant occurs ismoderated between a dense bed condition at about 320 kg/m³ (20 lb/ft³)and a transport flow regime at about 48 kg/m³ (3 lb/ft³). It is moredifficult to maintain a fast-fluidized flow at lower superficial gasvelocity because the catalyst tends to choke the reactant gas fed to thereactor, thereby jumping from a transport flow regime to a dense bed.Furthermore, at extremely high superficial gas velocities, no increasein catalyst flux will bring the flow regime out of transport. We havedetermined that a fast fluidized flow regime can be maintained under thepresent invention with superficial velocities as low as about 1.3 m/s (4ft/s) and as high as about 9.1 m/s (30 ft/s), which is higher thanconventionally used, and with catalyst fluxes as low as about 15 kg/m²s(2.8 lb/ft²s) and as high as about 1100 kg/m²s (204.5 lb/ft²s). In anembodiment, a very controllable fast fluidized regime can be maintainedunder the present invention with superficial velocities as low as about1.5 m/s (5 ft/s) and as high as about 5 m/s (16 ft/s) and with catalystfluxes as low as about 30 kg/m²s (5.6 lb/ft²s) and as high as about 325kg/m²s (60.4 lb/ft²s). Under these conditions, catalyst flux can beincreased or decreased to increase or decrease the space velocitywithout disrupting the flow regime such that it chokes to a dense bed oraccelerates into a transport flow regime.

[0046] The subject invention is useful in a catalytic conversion reactorin which catalyst is fluidized either by a fluidized feed or by afluidizing diluent or both. Typically, the fluidized feed has sufficientsuperficial velocity to entrain the catalyst or fluidize the catalyst asit enters into the reactor. In an embodiment of the present invention,the addition of diluent can be controlled to adjust the degree offluidization in the reactor.

[0047] The space velocity in the reactor section 12 may be controlled asfollows. The pressure drop between two elevations in the reactor section12 may be measured to monitor catalyst density in the reactor, weighthourly space velocity or other reactor condition that is proportional tospace velocity. When desired to adjust the space velocity, either tomaintain or attain the fast-fluidized regime, to change resultingconversion or selectivity or to accommodate a different feedcomposition, the control valve 20 can be opened relatively more or lessto change the catalyst flux which changes the space velocityaccordingly.

[0048]FIG. 1 illustrates a control scheme for effectuating adjustmentsto space velocity. A pressure sensor 92 is located at a relatively lowelevation in the reactor section 12, and a pressure sensor 94 is locatedat a relatively high elevation in the reactor section 12. In anembodiment, at least one of the sensors, preferably the lower pressuresensor 92, should be in the catalytic reaction zone 22. The pressuresensors 92, 94 transmit a pressure signal and/or other data to acontroller 96, which may comprise a pressure differential controller. Asensor 98 which may be on the line 36 or on the control valve 40determines the flow rate of feed therethrough by a suitable device andsignals data to the controller 96. With the data, the controller 96determines the mass flow rate of feed to the reactor 10 through thecontrol valve 40 and the mass of catalyst in the reactor section 12 fromwhich the weight hourly space velocity is determined. The flow rate offeed may be constant. The current weight hourly space velocity or aparameter proportional thereto is compared to a set point which can beadjusted. If the space velocity or proportional parameter does not matchthe set point, the controller 96 signals the control valve 20 to openrelatively more to lower the space velocity or to open relatively lessto increase the space velocity.

[0049] The temperature of the recycled spent catalyst in the recyclespent catalyst pipe 26 is similar to the temperature in the reactorsection 12. Hence, temperature in the reactor section 12 is controlledby the flow rate of hot regenerated catalyst in the regenerated catalystpipe 24 through the control valve 18. A temperature sensor 101 in thecatalytic reaction zone 22 or the reactor section 12 signal temperaturedata to a controller 100 which may be a temperature indicatorcontroller. The controller 100 compares the temperature in the reactorsection 12 to an adjustable set point temperature and signals thecontrol valve 18 to open relatively more if the reactor temperature islower than the set point or to open relatively less if the reactortemperature is higher than the set point. Suitable types, operation andlocations of sensors and controller(s) may vary consistently withordinary skill in the art and the description herein.

[0050] The volume of the catalytic reaction zone 22 is proportional toresidence time and inversely proportional to space velocity as indicatedby Formulas 5 and 10. The volume of the catalytic reaction zone 22 maybe adjusted and therefore residence time and space velocity may beadjusted in the catalytic reaction zone 22 by adjusting the flow rate ofa minimally reactive or non-reactive diluent to the reactor section 12.Additional diluent may be added to the reactor section 12 by a diluentline 102 at a rate governed by a control valve 104 through a nozzle 106.The effective reactor volume can be changed by adjusting the diluentrate to the reactor section 12 through the nozzle 106. If a smallereffective reactor volume is desired to provide a smaller residence timeor a larger space velocity, the control valve 104 should be openedrelatively more to allow a greater volumetric flow rate of diluent tothe reactor section 12 from the diluent line 102. If a larger effectivereactor volume is desired to increase residence time or reduce spacevelocity, the control valve 104 should be opened relatively less toallow a smaller volumetric flow rate of diluent to the reactor section12 from the line 102. Steam is a suitable diluent.

[0051]FIG. 2 shows another embodiment of the present invention whichcould be used to replace the reactor section 12 in FIG. 1. All elementsin FIG. 2 that are not modified from FIG. 1 retain the same referencenumeral designation. Although one reactor section 12′ may be used forcarrying out the purposes of this invention, the provision of aplurality of reactor subsections 84 with dedicated nozzles 88 andcontrol valves 40′ to govern the flow rate of feed to each of thereactor subsections 84 may offer flexibility over use of a singlereactor section 12. A plurality of the reactor subsections 84 within asingle reactor section 12′ provides a greater degree of control ofresidence time and space velocity. The embodiment in FIG. 2 providesgreater flexibility because the cross sectional area, and, therefore,the volume of a catalytic reaction zone 22′ are adjustable. Reactorcross-sectional area is inversely proportional to superficial gasvelocity. Superficial gas velocity is inversely proportional toresidence time and directly proportional to space velocity. Hence,residence time which is directly proportional to cross-sectional areaand space velocity which is inversely proportional to cross-sectionalreactor area may be modified by adjusting the flow rate or shutting offflow to one of the reactor subsections 84. The same relationship appliesto the reactor subsections 84 that do not have a constantcross-sectional area because the volume of the catalytic reaction zoneis proportional to residence time and inversely proportional to spacevelocity as shown in Formulas 5 and 10.

[0052] Reactant feed is distributed by a line 36′ at a flow rategoverned by the control valves 40′ through the nozzles 88 to therespective reactor subsections 84 in the reactor section 12′. Thereactor subsections 84 may be tubular with an open bottom end 90communicating with a dense catalyst bed 82 that forms in the reactorsection 12′. Feed entering the reactor subsections 84 preferably pullscatalyst from the dense catalyst bed 82 into the reactor subsections 84where contacting occurs. The amount of catalyst pulled into the reactorsubsection 84 for a given flow rate of feed in the nozzle 88 will beproportional to the superficial velocity of the feed and the height of acatalyst level 83 of the dense catalyst bed 82 which is controlled bythe control valves 18, 20. Hence, the ratio of catalyst to feed,catalyst density, catalyst flux, space velocity, and residence time inthe reactor subsections 84, and therefore the reactor section 12′, canall be controlled by adjusting the elevation of the catalyst level 83 ofthe dense catalyst bed 82 and/or adjusting or eliminating the flow rateof the feed through one or more of the control valves 40′.

[0053] The catalytic reaction zone 22′ comprises the reactor subsection84 from the bottom end 90 to a top region 44′. In an embodiment, thecatalytic reaction zone 22′ comprises all of the reactor subsections 84to which feed is distributed. The top region 44′ of each of the reactorsubsections 84 has a reduced cross-sectional area that may take the formof frustoconical or partial frustoconical sections. The reducedcross-sectional area of the top region 44′ serves to accelerate themixture of vapor product and spent mixed catalyst as they exit thereactor subsection 84. In an embodiment that is not shown, the topregions 44′ may communicate with outlet conduits which communicate thereactor subsections 84 with the transport conduit 46. In such anembodiment, the outlet conduits should all have a smallercross-sectional area than the respective reactor subsection 84 and thetransport conduit 46.

[0054]FIG. 3 is an upwardly looking cross-sectional view taken alongsegment 3-3 of the reactor section 12′. Although, four reactorsubsections 84 are shown in FIGS. 3 and 4, the invention contemplatesmore or less, but more than one reactor subsection 84. In an embodiment,the reactor subsections 84 may share common walls. In the embodimentshown in FIGS. 2 and 3, a cross-sectional area of the transport conduit46 may be less than the aggregate cross-sectional area of all of thereactor subsections 84 that feed the transport conduit 46. Additionally,in an embodiment, the cross-sectional area of the transport conduit 46may be less than that of a single reactor subsection 84, so that all butone of the reactor subsections 84 may be shut off. Consequently, uponleaving the reactor subsection 84, the product vapor and spent mixedcatalyst accelerate into a transport mode through the top region 44′,thus giving the spent catalyst and product vapor little time to furtherreact or crack into undesirable products. Entering transport mode alsoprevents catalyst from falling out of entrainment with the productvapor.

[0055] The alternative embodiment of a reactor 10′ of the presentinvention may be operated similarly to the reactor 10, but greaterflexibility is offered. The aggregate volume of catalytic reaction zone22′ of the reactor section 12 comprising the on-stream reactorsubsections 84 may be varied which is an additional way to adjust thespace velocity and the residence time. For instance, by cutting off flowthrough two of the control valves 40′ to two respective reactorsubsections 84, the volume of the catalytic reaction zone 22′ is halved.The change in volume will cancel out according to Formula 9. However,the halved cross-sectional area will double the superficial velocity forthe reactant feed at the constant flow rate through the line 36′.Moreover, because the catalyst brought into the reactor subsections 84is dependent on the flow of feed thereto which has doubled for eachreactor subsection remaining on-stream, the overall catalyst flux willnot substantially change. The doubled superficial velocity will drawdouble the catalyst flux into each of the two reactor subsections 84 tocompensate for the two reactor subsections 84 that have been shut off atthe control valves 40′. Hence, the weight hourly space velocity willincrease. Similarly, the change in volume cancels out in Formula 12while the velocity doubles. Consequently, the shutting off of flowthrough the control valves 40′ to two reactor subsections 84 results ina halving of the residence time in the reactor subsections 84.

[0056] Additionally, space velocity may be controlled by adjusting thecatalyst flux as in the reactor 10. The pressure drop between twoelevations in the catalytic reaction zone 22′ of the reactor section 12may be measured to monitor catalyst density in the reactor and weighthourly space velocity. When desired to adjust the space velocity or aparameter proportional thereto, without changing the flow rate througheither of control valves 40′, the control valve 20 can be openedrelatively more or less to change the height of the catalyst level 83.The height of the catalyst level 83 is proportional to the amount ofcatalyst flux pulled into the reactor subsections 84 which changes thespace velocity accordingly. FIG. 2 illustrates a control scheme foreffectuating adjustments to space velocity by changing flux. A pressuresensor 92′ is located at a relatively low elevation in the catalyticreaction zone 22 of each of the reactor subsections 84 or at least inthe one reactor subsection 84 that will always be on-stream, preferablyabove the nozzle 88. A pressure sensor 94′ is located at a relativelyhigh elevation in the reactor section 12′, in an embodiment, at alocation where all of the outlets of the reactor subsections 84converge, such as in the transport conduit 46, or in a single reactorsubsection 84 that will always be on-stream. The pressure sensors 92′,94′ transmit a pressure signal and/or other data to the controller 96,which may comprise a pressure differential controller. Sensors 98′ oneach of the branch lines from the line 36′, on each control valve 40′,on each of the nozzles 88 or on the line 36′ determine the flow rate offeed to the reactor section 12 by a suitable device and signals data tothe controller 96. With the data, the controller 96 determines the massflow rate of feed to the reactor 10 and the mass of catalyst in thecatalytic reaction zone 22′ comprising the on-stream reactor subsections84 from which the weight hourly space velocity is determined. The flowrate of feed through the line 36′ may be constant. The actual weighthourly space velocity in the reactor section 12 is compared to a setpoint which can be adjusted. If the space velocity does not match theset point, the controller 96 signals the control valve 20 to openrelatively more to lower the space velocity or to open relatively lessto increase the space velocity. Temperature in the reactor section 12 iscontrolled by the flow rate of hot regenerated catalyst in theregenerated catalyst pipe 24 through the control valve 18. Temperaturesensors 101 in the catalytic reaction zone 22′ signal temperature datato the controller 100 which may be a temperature indicator controller.The temperature sensor 98′ may instead be in the dense catalyst bed 82in the reactor section 12′. The controller 100 compares the temperaturein the reactor section 12′ to a set point temperature and signals thecontrol valve 18 to open relatively more if the reactor temperature islower than the set point or to open relatively less if the reactortemperature is higher than the set point. Locations of sensors,operation of controller(s) may vary consistent with ordinary skill inthe art and the description herein.

[0057] Some or all of the reactor subsections 84 may be operated underdifferent conditions, such as temperature, space velocity or residencetime to achieve the desired reactor flow conditions and productcomposition. Similarly, superficial feed velocity in one, some or all ofthe reactor subsections 84 may be different. Under this embodiment, thelower pressure sensors 92′ will have to be in each reactor subsection 84and the upper pressure sensor 94′ will have to be where all outlets ofreactor subsections converge or in each reactor subsection 84. Moreover,under this embodiment, the sensors 98′ will have to be on each branch ofthe line 36′ or on each of the control valves 40′.

[0058]FIG. 4 shows another embodiment of the present invention whichcould be used to replace the reactor section 12 in FIG. 1 or 12′ in FIG.2. All elements in FIG. 4 that are not modified from FIG. 1 retain thesame reference numeral designation. A reactor section 12″ of FIG. 4includes a plurality of reactant feed distributors 38 a-38 d all atdifferent heights in the reactor section 12″. Although four reactantfeed distributors 38 a-38 d may be used for carrying out the purposes ofthis invention, more or less may be used, but more than one. Eachreactant feed distributor 38 a-38 d is fed by a respective feed line 36a-36 d in communication with a main feed line 36″. A plurality ofcontrol valves 40 a-40 d are each dedicated to less than all of theplurality of reactant feed distributors 38 a-38 d to separately governthe flow of feed to the plurality of reactant feed distributors. In anembodiment, each control valve 40 a-40 d is dedicated to each respectivereactant feed distributor 38 a-38 d and feed line 36 a-36 d toseparately govern the flow rate of reactant feed therethrough. A sensor99 which may be on the main feed line 36″ or sensors 98 a-98 d which maybe on the respective lines 36 a-36 d or on the respective control valves40 a-40 d determines the flow rate of feed therethrough by a suitabledevice and signals data to the controller 96. A catalytic reaction zone22 a-22 d is the volume in the reactor section 12″ that is above therespective reactant feed distributor 38 a-38 d up to the top region 44.In the reactor section 12″, the reactor volume of the catalytic reactionzone 22 a-22 d is inversely proportional to the elevation of thereactant feed distributor 38 a-38 d.

[0059] The provision of a plurality of the reactant feed distributors 38a-38 d with the dedicated control valves 40 a-40 d to govern the flowrate of feed to the reactor section 12 may offer flexibility over use ofa single reactant feed distributor to control residence time and spacevelocity. The embodiment in FIG. 4 provides greater flexibility becausethe volume of the catalytic reaction zone 22 a-22 d is adjustable.Formula 5 indicates that space velocity is inversely proportional toreactor volume. Formula 10 indicates that residence time is directlyproportional to reactor volume. Although there will be a catalystdensity gradient over the reactor height which will change with thechanging height of the distribution of the reactant stream, the reactorvolume of the catalytic reaction zone will change more significantlyupon a change in feed distributor elevation.

[0060] If it is desired to reduce the residence time and/or increase thespace velocity in the reactor section 12′, the flow to the lowerreactant feed distributor 38 a-38 c through the dedicated control valve40 a-40 c would be shut off and flow to the higher reactant feeddistributor 38 b-38 d through the dedicated control valve 40 b-40 dwould be opened. Similarly, if it is desired to increase the residencetime and/or decrease the space velocity in the reactor section 12′, theflow to the higher reactant feed distributor 38 b-38 d through thededicated control valve 40 b-40 d would be shut off and flow to thelower reactant feed distributor 38 a-38 c through the dedicated controlvalve 40 a-40 c would be opened.

[0061] The top region 44 of the reactor sections 12″ have a reducedcross-sectional area that may take the form of frustoconical section.The reduced cross-sectional area of the top region 44 serves toaccelerate the mixture of vapor product and spent mixed catalyst as theyexit the reactor section 12″. Consequently, upon leaving the reactorsubsection 84, the product vapor and spent mixed catalyst accelerateinto a transport mode through the top region 44, thus giving the spentcatalyst and product vapor less time to further react or crack intoundesirable products. Entering transport mode also prevents catalystfrom falling out of entrainment with the product vapor.

[0062] Additionally, space velocity may be controlled by adjusting thecatalyst flux as in the reactor 10. The pressure drop between twoelevations in the catalytic reaction zone 22 a-22 d of the reactorsection 12 may be measured to monitor catalyst density in the reactorand weight hourly space velocity. When desired to adjust the spacevelocity or a parameter proportional thereto, without changing theelevation of the operating reactant feed distributor 38 a-38 d, thecontrol valve 20 can be opened relatively more or less to change thecatalyst flux to the reactor section 12″ which changes the spacevelocity accordingly. FIG. 4 illustrates a control scheme foreffectuating adjustments to space velocity by changing flux which issimilar to that for FIG. 1. Although only one is shown, the pressuresensors 92′ will be located at a point slightly above every reactantfeed distributor 38 a-38 d in the respective reaction zone 22 a-22 d.The pressure sensor 94 is located at a relatively high elevation in thereactor section 12′. The pressure sensors 92′, 94′ transmit pressuresignals and/or other data to the controller 96, which may comprise apressure differential controller. The sensor 99 determines the flow rateof feed through to the applicable reactant feed distributor 38 a-38 d bya suitable device and signals data to the controller 96. With the data,the controller 96 determines the mass flow rate of feed to the reactor10 through the reactant feed distributors 38 a-38 d and the mass ofcatalyst in the reactor section 12 from which the weight hourly spacevelocity is determined. The flow rate of feed through the line 36″ maybe constant. The actual weight hourly space velocity in the reactorsection 12″ is compared to a set point which can be adjusted. If thespace velocity does not match the set point, the controller 96 signalsthe control valve 20 to open relatively more to lower the space velocityor to open relatively less to increase the space velocity to come closerto the desired space velocity. Temperature in the reactor section 12 iscontrolled by the flow rate of hot regenerated catalyst in theregenerated catalyst pipe 24 through the control valve 18 based on asignal from a temperature sensor (not shown) in the catalytic reactionzone 22 a-22 d to the controller 100 similar to the control scheme shownin FIG. 1. Suitable locations, types and operation of sensors andcontroller(s) may vary consistent with ordinary skill in the art and thedescription herein.

[0063] It is also contemplated that one or more distributors 38 a-38 dmay operate at the same time at the same or different flow rates toprovide desired benefits. Additionally, if diluent through the nozzle 32is not sufficient to fluidize catalyst up to the higher reactant feeddistributor 38 a-38 d, a lower distributor may have to always operate tosome degree to fluidize catalyst up to the primarily operationalreactant feed distributor 38 a-38 d. Lastly, a retractable distributor(not shown) or a transport conduit with a telescopically retractableinlet end (not shown) may be used to accomplish the present invention.

[0064] Accordingly, the present invention provides for the adjustment ofreactor flow parameters of residence time, volume and space velocity tomeet particular needs in response to differences in feed composition ordesired product slate and to achieve and maintain an appropriatefluidization regime.

What is claimed is:
 1. A catalytic reactor for the catalytic conversionof a feed stream by contact with fluidized catalyst particles to producea product stream, said reactor comprising: a reactor section defining acatalytic reaction zone and a feed inlet communicating with the reactionzone; a separation section for separating gaseous products fromfluidized catalyst particles, said separation section defining aparticle outlet for discharging fluidized catalyst particles and saidseparation section defining a gas recovery outlet for withdrawing saidgaseous products from the separation section; a disengaging conduitextending from the reactor section to the separation section, in fluidcommunication with the reaction zone, for conducting the product streamand fluidized catalyst particles and defining a discharge opening fordischarging the product stream and fluidized catalyst particles; atleast one catalyst circulation pipe for conveying fluidized catalystparticles to the reactor section, and a catalyst control valve on saidcirculation pipe for controlling the rate at which catalyst particlesare added to the reactor section; and a feed conduit for adding feed tosaid catalytic reaction zone; wherein said catalyst control valve isoperable to control the space velocity in the reactor.
 2. The catalyticreactor of claim 1 wherein said reactor section further comprises acatalyst mixing zone below said reaction zone in fluid communicationwith said circulation pipe.
 3. The catalytic reactor of claim 2 whereinsaid at least one catalyst circulation pipe is in fluid communicationwith said catalyst mixing zone.
 4. The catalytic reactor of claim 1wherein said catalyst mixing zone comprises a pot below said reactionzone.
 5. The catalytic reactor of claim 1 wherein a pressuredifferential indicator with sensors at two elevations in said reactorsection is linked to said catalyst control valve.
 6. The catalyticreactor of claim 5 including an additional catalyst circulation pipewith one end in communication with said reactor section and another endin communication with a catalyst regenerator, a control valve on saidadditional catalyst circulation pipe being governed by the temperaturein said reactor section.
 7. The catalytic reactor of claim 1 whereinsaid catalyst circulation pipe is in communication with the separationsection.
 8. The catalytic reactor of claim 1 wherein the reactor sectioncomprises a plurality of discrete reactor subsections.
 9. The catalyticreactor of claim 8 wherein a reactant feed line is in communication witheach reactor subsection and a dedicated control valve in communicationwith each reactor subsection to separately regulate feed to each reactorsubsection.
 10. A process of catalytically reacting a feed by contactingit with catalyst particles at a controlled space velocity, said processcomprising: delivering catalyst particles to a reactor section at a ratesufficient to provide a catalyst flux of between about 15 and about 1100kg/m²s and a catalyst density in the reactor section between 48 and 320kg/m³ upon fluidization; distributing a reactant stream to said reactorsection at a rate sufficient to provide a superficial velocity ofbetween about 1 m/s and about 9 m/s, that will fluidize the catalystparticles and contact the reactant stream with catalyst particles,contacting said catalyst particles with said reactant stream; catalyzingthe conversion of the reactant stream to a product stream; andwithdrawing catalyst particles and product fluid, including said productstream, from the reactor.
 11. The process of claim 10 further includingcirculating withdrawn catalyst particles back to said reactor section.12. The process of claim 11 further including adjusting a space velocityin the reactor section.
 13. The process of claim 12 wherein the spacevelocity is adjusted by adjusting the catalyst flux in the reactorsection.
 14. The process of claim 13 wherein the catalyst flux isadjusted based on the catalyst density in the reactor section.
 15. Theprocess of claim 11 wherein the space velocity is adjusting by adjustinga volume of a catalytic reaction zone in said reactor section.
 16. Theprocess of claim 11 wherein the catalyst flux is between about 25 andabout 300 kg/m²s.
 17. The process of claim 11 wherein the superficialvelocity is between about 1.5 and about 5 m/s.
 18. A process ofcatalytically reacting a feed by contacting it with catalyst particles,said process comprising: delivering catalyst particles to a reactorsection at a catalyst circulation rate to provide a catalyst fluxsufficient to provide a catalyst density in the reactor section uponfluidization; distributing a reactant stream to the reactor section at arate sufficient to fluidize the catalyst particles and contact thereactant stream with catalyst particles; contacting said catalystparticles with said reactant stream; catalyzing the conversion of thereactant stream to a product stream; measuring a pressure drop in saidreactor section; controlling the catalyst circulation rate in responseto the pressure drop in the reactor section; and withdrawing catalystparticles and said product stream from the reactor section.
 19. Theprocess of claim 18 wherein a reactant stream is distributed to at leastone of a plurality reactor subsections in the reactor section andchanging the reactor subsections to which a reactant stream isdistributed.
 20. The process of claim 18 wherein an additional catalystcirculation rate of regenerated catalyst particles to said reactorsection is controlled in response to a temperature in the reactorsection.